Saracens, semi-finalists last season when they were outsmarted by Toulon at Twickenham, look to have the best prospect of making the knockout stage. They are grouped with Toulouse, four-times winners but wobbling of late, Connacht and Zebre, who went through their first campaign in the RaboDirect without winning a match, an achievement they also managed in their Heineken Cup pool.

Leicester almost invariably draw Treviso, no longer easybeats in Europe, but they will face Montpellier, who made the Top 14 play-offs last month, for the first time. They will also be returning to a ground where they have suffered their two heaviest defeats in the tournament, Ravenhill, having lost to Ulster 33-0 in 2003 and 41-7 eight seasons later.

Northampton, finalists in 2011, have probably the most demanding assignment. They were drawn with Leinster, the RaboDirect Pro 12 and Amlin Challenge Cup champions who beat them in Cardiff two years ago, the Top 14 champions Castres, who are grouped with the Saints for the third successive campaign, and Ospreys, the one Welsh region which in recent seasons has looked threatening in Europe.

"It is a very tough draw for us," said the Northampton director of rugby, Jim Mallinder. "Leinster have proved time and again in the last few years that they are one of the top teams in European rugby, Ospreys have won the Pro 12 twice in the last four years and have five Lions in their squad and we know that Castres will be as tough as they come. All six matches will be tough and we will do doing our hardest to make the knock-out stage."

Toulon, the holders, are grouped again with Cardiff Blues, but their most testing games are likely to come at Exeter and Glasgow, while Gloucester are fittingly in a pool of teams that have been inconsistent in recent seasons, Munster, Perpignan and Edinburgh.

"We are happy with the draw," said the Gloucester chief executive, Stephen Vaughan. "Munster are one of the giants of Europe, Perpignan have a couple of our former players, Luke Narraway and Alasdair Strokosch, and Edinburgh made the semi-finals last year. We want to be competitive at this level, hence our pre-season programme this year which is deigned to prime us to this level of rugby."

Harlequins will not feel much better than Northampton, finding themselves with last month's beaten finalists Clermont Auvergne, big-spending Racing-Métro, who have signed the Lions Jonathan Sexton, Jamie Roberts and Dan Lydiate, and the Scarlets. In the Amlin Challenge Cup, Sale and Worcester are in the same group, along with the 2012 winners Biarritz, Wasps will face Bayonne again, while newly promoted Newcastle's fate will depend on how they fare home and away against another club returning to the top flight, Brive.